Insulated magnetic core and method of making insulated magnetic cores



April 6, 19 7. R, ms 2,076,230

I INSULATED MAGNETIC GORE AND METHOD OF MAKING INSULATED MAGNETIC CORES Filed Dec. 14, 1935 (2754M!!! GMT/N6 Patented Apr. 6, 1937 PATENT OFFICE INSULATED MAGNETIC CORE AND METHOD OF MAKING CORES INSULATED MAGNETIC Randall Gillis, La Grange, Ill., assignor to Western Electric Company,

Incorporated, New York,

N. Y., a corporation of New York Application December 14, 1933, Serial No. 702,289

6 Claims.

This invention relates to insulated magnetic cores and methods of making insulated magnetic cores and more particularly to magnetic cores of the compressed dust type having an integral insulating coating and methods of making such COIES.

Objects of the invention are to provide effective and efficient insulated magnetic cores and effective and economical'methods of making such 10 cores.

In accordance with one embodiment of the invention, a magnetic core made of compressed finely divided magnetic particles is sprayed with an aqueous solution of lead borate and dried. The

coated core is then heated to a temperature sufflciently high to fuse the coating to form a glazed vitreous insulated coating-on the core.

Other features and advantages of the invention will become apparent from the following detailed descriptions, reference being bad to the accompanying drawing, wherein Fig. 1 is a perspective view insulated coating made in accordance with the invention, and

Fig. 2 is a fragmentary sectional view of the core shown in Fig. 1.

In carrying out the present inventionthe magnetic material is preferably prepared from brittle alloys containing various percentages of nickel and iron. These alloys may be prepared as fully described in the patent to C. P. Beath and H. M. E. Heinicke, No. 1,669,649, issued May 15, 1928.

An alloy thus prepared is rolled while hot into 'relatively thin slabs and quenched to produce a fine crystalline structure, which is very desirable since the distintegration of the material takes place at the crystal boundaries and consequently the smaller the size of the crystals, the finer the dust which can be produced from the finished product. The magnetic alloy thus received in slab form is reduced to a finely divided form or dust, in any well known manner, as for example, in a hammer mill or other suitable reducing apr paratus and subsequently pulverized in an attri tion mill.

The dust from the attrition mill is sifted and the portion passing through a 120 mesh sieve is placed in a closed container and annealed at a temperature of approximately 885 C. The annealed dust is removed from the container in the form of a cake which is again reduced to a powder by crushing in a rotary crusher and subsequently grinding in an attrition mill. The ground dust is again sifted through a standard 120 mesh of a core having an screen and the dust passing through such a screen is insulated with a solution of chromic acid, sodium silicate, powdered talcum and water. This mixture is heated and stirred until dry, as fully described in Patent No. 1,669,643, issued May 15, 1928, to J. W. Andrews and R. Gillis. As clearly described therein, the desired permeability can be obtained by varying the amount of the insulating material. Obviously, other methods of insulating the dust, well known to the art, could also be employed.

The insulated dust is sifted through a 16 mesh screen and placed in a mold and compressed into core parts under a pressure of approximately 200,000 pounds per square inch. The core parts are then covered with a ceramic slip either by dipping or spraying the slip on the parts. The ceramic material may consist of 83 parts of red lead and 17 parts'of boric acid. A suspending agent, such as ammonium alginate, may be used to form an aqueous colloidal solution for dipping or spraying the parts.

Another composition which has been found to be effective for this purpose comprises red lead 125 parts, boric acid 63 parts, flint parts, cryolite 15 parts, iron oxide 10 parts, soda ash '1 parts, tin oxide 5 parts, zinc oxide 4 parts, manganese dioxide 1.04 parts, cobalt oxide 1.16 parts.

The cores thus coated are then heated at a temperature from 575 C; to 690 C., which is sufflcient to fuse these low'melting point ceramic compositions. During this heat-treatment the cores are also annealed to relieve the stresses arising from the compression of the dust particles into cores and the annealing temperature must be low enough not to damage the insulating material on the dust particles. During this annealing heat-treatment the ceramic coating protects the core material from the atmosphere and prevents oxidation of the materials which effects a considerable decrease in the hysteresis losses of the cores and improves their permeability. Improvements of the order of 20% in hysteresis losses have been noted in cores treated in this manner over cores annealed in the atmosphere. In additionto the improvement in the magnetic characteristics of the cores in spraying or coating the cores with vitreous enamel during the an ealing of the cores, the enamel serves as an insulating material for the cores. In accordance with one practice used in the manufacture of loading coils, it is customary to apply a serving of paper to the cores before applying the windings thereto. The present invention eliminates the necessity for wrapping the core with paper or other insulating material and the windings may be wound directly on the insulating cores.

While several types of vitreous enamels have been referred to, it is obvious that any of the low fusing point enamels may be used and the enamels described are merely illustrative of the invention.

What is claimed is:

1. A method 0! making magnetic cores by pressing individually insulated magnetic particles into a mass, applying an additional ceramic envelop around the formed mass oi magnetic material, and applying heat to fuse the ceramic envelop and anneal the magnetic particles.

2. A magnetic core comprising a compressed mass of finely divided insulated magnetic particles and a fused ceramic insulating coating over the core, the particles being insulated with ma terial having a different composition than the core coating material, and the core coating material having a fusing temperature within the annealing range of the magnetic particles.

3. A core comprising particles of metal individually coated with insulating material and pressed into form and a fused envelop of a different insulating material having a fusing temperature of the same order as the annealing temperature of the metal particles.

4. A method of making cores comprising coating finely divided magnetic particles with insu lating material, pressing the coated particles into a mass, applying to the mass a ceramic slip having a lower fusing temperature than the destructive temperature of the insulation on said particles, and heating the cores to fuse the slip and anneal the cores.

5. A magnetic core comprising a compressed mass of finely divided magnetic particles individually coated with insulation compounded 01 a metallic silicate and talcum, and a fused ceramic insulating coating over the core, the ceramic coating having a fusing temperature within the annealing range of the magnetic particles.

6. A method oi making magnetic cores by pressing individually insulated magnetic particles into a mass, applying an additional envelope of lead borate around the formed mass of magnetic material, and applying heat to fuse the lead borate and anneal the magnetic particles.

RANDALL GILLIS. 

